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IE433 CAD/CAM

Computer Aided Design andComputer Aided Manufacturing

Part-4

Computer Graphics-CAD Software

Industrial Engineering Program

King Saud University



CAD Software

CAD software can be divided based upon thetechnology used:

1. 2-D drawing. Its applications include,

· mechanical part drawing

· printed-circuit board design and layout· facilities layout

· cartography

2. Basic 3-D drawing (such as wire-frame modelling)

3. Sculptured surfaces (such as surface modelling)4. 3-D solid modelling

5. Engineering analysis



Geometric Modeling

Geometric modelling refers to a set of

techniques concerned mainly with

developing efficient representations of geometric aspects of a design. Therefore,

geometric modelling is a fundamental part

of all CAD tools.



Geometric modeling is the basic of manyapplications such as:

•Mass property calculations.

• Mechanism analysis.

• Finite-element modelling.

•NC programming.

Requirements of geometric modelling include:

• Completeness of the part representation.

•

The modelling method should be easy to use by designers.• Rendering capabilities (which means how fast the entities

can be accessed and displayed by the computer).



Geometric Modeling Approaches

The basic geometric modelling approaches available to

designers on CAD/CAM systems are:

1. Wire-frame modeling.2. Surface modeling.

3. Solid modeling.



Wire-frame Modeling

Wire-frame modelling uses points and curves

(i.e. lines, circles, arcs), and so forth todefine objects.

The user uses edges and vertices of the part

to form a 3-D object

Wire-frame model part



Example



Surface Modeling

Surface modeling is more sophisticated than wireframe modeling

in that it defines not only the edges of a 3D object, but also its

surfaces.

In surface modeling, objects are defined by their bounding faces.

Examples



SURFACE ENTITIES

Similar to wireframe entities, existing CAD/CAM

systems provide designers with both analytic andsynthetic surface entities.

Analytic entities include :

•Plane surface,

•

Ruled surface,•Surface of revolution, and

•Tabulated cylinder.

Synthetic entities include

•The bicubic Hermite spline surface,•B-spline surface,

•Rectangular and triangular Bezier patches,

•Rectangular and triangular Coons patches, and

•Gordon surface.



Plane surface. This is the simplest surface. It requires

three noncoincident points to define an infinite plane.



Ruled (lofted) surface. This is a linear surface. It interpolates

linearly between two boundary curves that define the surface

(rails). Rails can be any wireframe entity. This entity is ideal to

represent surfaces that do not have any twists or kinks.



Surface of revolution. This is an axisymmetric surface

that can model axisymmetric objects. It is generated by

rotating a planar wireframe entity in space about the axisof symmetry a certain angle.



Tabulated cylinder. This is a surface generated by

translating a planar curve a certain distance along a

specified direction (axis of the cylinder).



Bezier surface. This is a surface that approximates given

input data. It is different from the previous surfaces in

that it is a synthetic surface. Similarly to the Bezier curve,it does not pass through all given data points. It is a

general surface that permits, twists, and kinks . The

Bezier surface allows only global control of the surface.



B-spline surface. This is a surface that can approximate

or interpolate given input data (Fig. 6-9). It is a synthetic

surface. It is a general surface like the Bezier surface butwith the advantage of permitting local control of the

surface.



Solid Modeling

Solid models give designers a completedescriptions of constructs, shape, surface, volume,

and density.



In CAD systems there are a number of representation schemes for solid modeling

include:

•Primitive creation functions.

•Constructive Solid Geometry (CSG)

•Sweeping

•Boundary Representation (BREP)



Primitive creation functions:

These functions retrieve a

solid of a simple shape from

among the primitive solidsstored in the program in

advance and create a solid of

the same shape but of the

size specified by the user.



Constructive Solid Geometry (CSG)

CSG uses primitive shapesas building blocks and

Boolean set operators (U

union, difference, and

intersection) to constructan object.



Example



Sweeping

Sweeping Sweeping is

a modeling function in

which a planar closed

domain is translated or

revolved to form a

solid. When the planardomain is translated,

the modeling activity is

called translational

sweeping; when the

planar region isrevolved, it is called

swinging, or rotational

sweeping.



Boundary Representation

Objects are represented by their bounded faces.



B-Rep Data Structure







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